The present invention relates to an electrophotographic photoreceptor for use in electrophotographic apparatuses wherein a latent image is formed by exposing the electrophotographic photoreceptor to light. Although the present invention is useful in analogue and digital electrophotographic apparatuses, it is especially suitable for digital electrophotographic apparatuses, wherein a latent image is formed by exposing the electrophotographic photoreceptor to light that is based on image signals that have been converted to digital data. More particularly, this invention relates to an electrophotographic photoreceptor which gives a photodecay curve having a threshold value and in which the exposure energy required for transitions from a high to a low surface potential changes little (high-xcex3 characteristics). The so-called xe2x80x9cS-shapexe2x80x9d photodecay is characterized by the occurrence of very little or no photodecay until the exposure energy reaches a particular level, at which a sharp photodecay is observed. The photodecay curve has a reverse xe2x80x9cSxe2x80x9d shape. High-xcex3 characteristics are symbolized as S-shape photodecay.
In the development of electrophotographic processes such as the Carlson process, the primary object is typically to describe an original image in an analogue manner. In order for a photoreceptor to faithfully reproduce intensity differences of an inputted light as toner density differences in a toner image, the surface potential of the photoreceptor typically decreases in proportion to the amount of light to which it exposed. Accordingly, photoreceptors typically include photosensitive materials having so-called xe2x80x9clow-xcex3xe2x80x9d characteristics. Such low-xcex3 photoreceptors are akin to simple photoconductors, and are employed in the initial techniques of electrophotography; and these include photosensitive layers based on amorphous selenium (Se), amorphous silicon (Si) and ZnO-binder layers formed so as to akin to amorphous selenium layers.
xe2x80x9cFunctionally separatedxe2x80x9d photoreceptors have been developed, which employ separate charge generation and charge transport materials for improved charge generation efficiency and better transport efficiency. Examples of the functionally separated photoreceptors include layered photoreceptors having both charge generation and charge transport layers, and the later-developed photoreceptors having organic semiconductors.
In recent years, however, electrophotography has become increasingly linked to computers and electronic communications, and the recording techniques employed in printers and facsimile telegraphs have rapidly shifted to electrophotography. Ordinary copiers are beginning to employ a recording technique that enables image processing techniques such as reversal, cutting and blinding. Because of these recent developments, electrophotographic recording techniques are shifting from the conventional analogue recording for plain paper copiers to digital recording.
As described above, typical photoreceptors currently employed in electrophotographic devices, which are based on analogue signals, have low-xcex3 characteristics. These low-xcex3 photoreceptors are unsuitable for use in electrophotographic processes wherein the inputted digital light signal is outputted as a digital image, as in computer printers, digital copiers and other devices wherein the image is processed digitally. It is believed that because low-xcex3 photoreceptors contain a conventional photosensitive material, they cannot reproduce an original digital image, since the photoreceptors faithfully form images attributable not only to the deterioration of digital signals occurring in the signaling channel extending from a computer or image processor to the electrophotographic apparatus, but also to aberrations of the optical system used for condensing a light beam for writing or forming an image of an original. Accordingly, there is a strong desire for a electrophotographic photoreceptor having both high sensitivity and high-xcex3 characteristics.
Under these circumstances, a high-xcex3 photoreceptor is disclosed in unexamined published Japanese patent application JP-A-1-169454. The referenced high-xcex3 photoreceptor undesirably is a positive charging photoreceptor, that is, the polarity of the photoreceptor in a charged state is opposite to that of the charged photoreceptors employed in existing electrophotographic printers (negative charging). Accordingly, the referenced photoreceptor requires a toner or developer material that is undesirably of the opposite polarity with respect to the conventional charge, which undesirably increases the burden on apparatus development. In addition, since the referenced photoreceptor is a single layer type, the properties of the charge generation material, which is present in an outermost part of the photoreceptor, undesirably deteriorates by the action of an active gas, e.g., ozone.
JP-A-6-83077, JP-A-9-96914 and JP-A-9-160263 propose functionally separated, negative charging photoreceptors having high-xcex3 characteristics. These photoreceptors, however, employ a specific charge transport polymeric compound, and also the charge transport layer needs to be heterogeneous, which inhibits the freedom of material selection and limits the possibility of future development and industrialization.
An object of the present invention is to provide a negative charging electrophotographic photoreceptor having high-xcex3 characteristics, long life and high stability, which make the photoreceptor suitable for repeated use.
These and other objects have been attained by the present invention, the first embodiment of which provides a negative charging electrophotographic photoreceptor, which includes:
an electroconductive substrate;
a charge generation layer disposed on the electroconductive substrate; and
a charge transport layer disposed on the charge generation layer;
wherein the charge transport layer is in a homogeneous state; and wherein the charge generation layer has a light transmittance of at least 10% per micrometer of film thickness of the charge generation layer.
Another embodiment of the invention provides a negative charging electrophotographic photoreceptor, which includes:
an electroconductive substrate;
a charge generation layer disposed on the electroconductive substrate; and
a charge transport layer disposed on the charge generation layer;
wherein the charge transport layer is in a homogeneous state; and wherein the photoreceptor has an E50/E10 ratio in the range of 1 to 6.
Another embodiment of the invention provides a negative charging electrophotographic photoreceptor, which includes:
an electroconductive substrate;
a charge generation layer disposed on the electroconductive substrate; and
a charge transport layer disposed on the charge generation layer;
wherein the charge transport layer is in a homogeneous state; and wherein the charge generation layer has a light transmittance of at least 68% per micrometer of film thickness of the charge generation layer.
Another embodiment of the invention provides a process for producing the electrophotographic photoreceptor of the invention, which includes solvent coating the charge transport layer onto the charge generation layer, wherein the charge generation layer is insoluble in the solvent.
Another embodiment of the invention provides an electrophotographic apparatus, which includes the electrophotographic photoreceptor of the invention.
Another embodiment of the invention provides a method of forming an image, which includes exposing the electrophotographic photoreceptor of the invention to light.
Another embodiment of the invention provides a method for optimizing an E50/E10 ratio in an electrophotographic photoreceptor to obtain S-shaped, high-xcex3 characteristics in the electrophotographic photoreceptor, the electrophotographic photoreceptor including:
an electroconductive substrate;
a charge generation layer disposed on the electroconductive substrate and containing a charge generation material and a binder resin; and
a charge transport layer disposed on the charge generation layer and containing a charge transport material and a binder resin;
which process includes correlating the following factors:
charge generation material;
concentration of charge generation material;
binder resin in the charge generation layer;
charge transport material;
concentration of charge transport material; and
binder resin in the charge transport layer.
Another embodiment of the present invention provides an electrophotographic apparatus, which includes:
an electrophotographic photoreceptor; and
an exposure light, wherein
the electrophotographic photoreceptor includes:
an electroconductive substrate;
a charge generation layer disposed on the electroconductive substrate; and
a charge transport layer disposed on the charge generation layer;
wherein the charge transport layer is in a homogeneous state; and wherein the charge generation layer includes a light transmittance to the exposure light of at least 10% per micrometer of film thickness of the charge generation layer.
Another embodiment of the present invention provides a method of forming an image, which includes exposing the above electrophotographic photoreceptor to the exposure light.